What is the difference between a benign brain tumor and a malignant (cancerous) brain tumor?

No mets or invasion: Benign tumors do not metastasize or invade adjacent structures. They typically slowly grow locally and cause symptoms that is very much related to the location of the tumor. For example tumor and presses on acoustic nerve, can cause hearing difficulty.

Hard question: Any brain tumor can be malignant by position. Even if benign but in vital region is bad. A malignant metastasis may be easy to remove and cured by cure of the source. A primary malignant brain tumor may be easy to remove and cure or can be diffuse and impossible to remove or cure.